1. Field of the Invention
The invention pertains to a method and a device for compensation in a measurement of a magnetic field. The invention also pertains to a method and a system for localizing an object as well as an information-recording medium, to implement these methods.
2. Prior Art
The present filing party knows a method for compensation in a measurement of a magnetic field comprising the emission, in the presence of a magnetic disturber, of a magnetic field by a uniaxial source situated on one side of the magnetic disturber, the magnetic moment of this source being known.
A magnetic disturber is defined herein as any object that degrades or deforms the field lines of a magnetic field emitted in proximity. For example, the disturber may be a conductive part. In this case, the degradation of the magnetic field lines is caused by the appearance of eddy currents in the conductive part. The conductive part may be for example a metal part. The disturber may also be a magnetic part such as a paramagnetic or ferromagnetic part. A part is considered to be magnetic if its relative permeability is different from 1.
Compensation in a measurement of a magnetic field is done by correcting this measurement to make it approach the measurement that would be obtained in the absence of the magnetic disturber.
A uniaxial magnetic field source is a source that preferably emits the magnetic field along only one axis. For example, a coil whose turns are wound about a same axis is a uniaxial magnetic field source and the preferred emission axis coincides with the winding axis of the turns.
A triaxial or three-axis magnetic field source emits a magnetic field along three emission axes that are mutually non-collinear. For example, such a source or emitter is formed by several uniaxial magnetic field sources that are aligned respectively on each of the axes of emission.
Similarly, an at least triaxial source is a source that emits magnetic fields along three or more non-collinear axes.
A triaxial magnetic field sensor is also defined as a sensor capable of measuring the direction of the magnetic field. Typically, to this effect, these sensors measure the amplitude of the projection of the magnetic field on three mutually non-collinear axes of measurement. Thus, these sensors can be used to measure the direction of the magnetic field and, generally, also the amplitude of this magnetic field.
Methods of compensation in the measurement of the magnetic field are used particularly in methods for localizing an object by means of a magnetic system. Indeed, if the measured magnetic field used to localize an object is disturbed, then the localizing of the object is erroneous. This may have particularly deleterious consequences when the localizing method is used in medicine to locate a probe or a catheter within the human body. Indeed, for such applications, it is very important that the localization of the probe should be reliable. Now, in medicine, there are many magnetic disturbers that are liable to falsify the localization. For example, the magnetic disturber may be an operation table, the metal frame of another apparatus placed near the patient, etc.